Ligand field theory, application energy difference

The most interesting applications of ligand field theory have been made when there are several non-bonding electrons. Consider, for instance, an atom or ion with five d electrons in an octahedral ligand field. When the field is weak the electrons will, as in the free atom, occupy different orbitals singly (Fig. 77(a), (b)). But if the field is increased, the dy electrons will eventually fall into d orbitals, the drop in orbital energy outweighing the increase in mutual repulsion of the electrons (Fig. 77(c)). The occupation... 

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